In recent memory hard disk drives, high storage capacity and miniaturization have been demanded. In order to increase the recording density, it has been strongly urged to lower flying height of a magnetic head and to reduce the unit recording area. Along with this trend, the surface qualities required after polishing have become severely assessed every year even in a process for manufacturing a substrate for a magnetic disk. In order to satisfy the lowering of flying height of the magnetic head, the surface roughness, the microwaviness, the roll-off and projections are reduced, and in order to satisfy the reduction in unit recording area, the sizes and depths of the scratches and pits allowed have become increasing smaller.
In order to meet such requirements, there has been known a polishing composition for an aluminum disk substrate, containing colloidal silica particles having different mono-modal number particle size distributions, whereby an aluminum disk substrate having a smaller average waviness and fewer surface defects can be obtained (see, for instance, Japanese Patent Laid-Open No. 2002-30274).
In addition, there has been known a polishing composition containing colloidal silicas having a specified particle size distribution, which has excellent surface smoothness, whereby polishing can be carried out at an economical rate without generating surface defects (see, for instance, Japanese Patent Laid-Open No. 2001-323254).
However, with the increase in improvements in the recording densities over the years, since the flying height of the magnetic head must be lowered, the specification for microwaviness desired for a substrate is becoming increasingly stricter. Therefore, in the conventional combinations of the polishing composition with the conventional polishing pad described in the above-mentioned Japanese Patent Laid-Open Nos. 2002-30274 and 2001-323254, the quality of the substrate cannot be achieved.
In addition, Japanese Patent Laid-Open No. 2001-62704 discloses a method of reducing microwaviness using a pad without pores on the surface of the polishing pad. In this method, there arises a problem such as the polishing rate is delayed because the polishing liquid is not sufficiently retained in the polishing pad.
On the other hand, in the field of semiconductors, the trends of producing thinner wiring have been progressed along with the trends of highly integrated circuits and higher speed at the operating frequencies. Even in the method for manufacturing a semiconductor device, since the focal depth becomes shallow with the trend of thinning the wiring during the exposure of a photoresist, further smoothening of a pattern-forming surface has been desired.
In order to meet such requirements, there have been proposed polishing compositions with improved surface qualities such as surface roughness Ra and Rmax, scratches, pits and projections (Japanese Patent Laid-Open Nos. Hei 9-204657, Hei 11-167715 and Hei 11-246849). With the increase in improved recording densities over the years, the chamfer in the texture step, which is a after treatment step, is reduced, so that the allowable level of scratches after the polishing step of the substrate has becoming increasingly stricter. Therefore, in the conventional combinations of the polishing composition with the polishing pad, the scratches cannot be sufficiently removed, so that a desired quality cannot be achieved.